The Japanese prime minister, Taro Aso, today dissolved parliament and called a general election for 30 August that could see his party cast out of power for only the second time in almost 55 years.

Racked with infighting and policy confusion during Aso's 10 months in charge, the Liberal Democratic party (LDP) trails the main opposition Democratic Party of Japan (DPJ) in opinion polls by what many believe is an insurmountable margin.

Aso, the manga-addicted scion of a wealthy political dynasty, has presided over one of the LDP's most miserable periods in power since he took office last September.

He has managed to insult teachers, the elderly and Alzheimer's sufferers with ill-judged comments, at one point likening the opposition to the Nazis. His cabinet has been dogged by scandal, including the resignation in February of his finance minister, Shoichi Nakagawa, after he turned up drunk at a G8 press conference in Italy.

A poll in yesterday's Mainichi newspaper put support for the DPJ at 56%, with 23% backing the LDP. At a meagre 11%, support for Aso trailed well behind that for the DPJ's leader, Yukio Hatoyama, on 28%.

Though his party's policies are short on detail, Hatoyama has struck a chord with disaffected voters with promises to take on the reform-resistant bureaucracy, lower taxes and set aside cash for families, the sick and the elderly.

The DPJ has also vowed to pursue a more independent foreign policy after decades of subservience to the US, and to increase its involvement in UN peacekeeping missions.

Hatoyama told party members that the election would be a "revolutionary" opportunity for politicians to wrest control from bureaucrats, who have dominated policymaking under the LDP. "We should face it with a sense of historic mission," he said.

Japan has effectively been in a state of political paralysis since the DPJ took control of the upper house in 2007, giving it the ability to block and delay government legislation.

Yet despite its comfortable lead in the opinion polls, the DPJ are by no means assured of taking control of the more powerful lower house.

The LDP holds 303 seats in the 408-seat chamber – and its junior coalition partner New Komeito holds 31 – while the DPJ has just 112. The result, analysts say, will be determined by the roughly 30% of voters who remain undecided.

Aso, 68, has been criticised for his handling of Japan's recession with the economy faring even worse than those of the US and the EU. Record stimulus packages have been derided as wasteful, at a time when Japan is lumbered with a public debt equivalent to 180% of its GDP.

His party also appears poorly equipped to address pressing social problems, including how to fund the creaking state pension and healthcare for the elderly.

Public disaffection with the LDP, one of the most successful electoral machines in modern political history, culminated in a resounding defeat at last weekend's elections for the Tokyo assembly, the party's first loss in the capital for 40 years.

That defeat triggered an attempt by LDP rebels to out Aso before the election, but the move was frustrated by party executives desperate to impose a semblance of unity in the run-up to the general election.

After insisting that the LDP's drubbing in Tokyo was not an indictment of his administration, Aso apologised to party colleagues for his mistakes as leader.

"I'm sorry for my lack of ability and that I couldn't fully unite the party," he said. "We must sincerely accept the public's criticism, humbly reflect on our performance and start afresh."